There is a growing interest in the art in the development of polymeric materials which have good strength and retain a considerable portion of their strength after extended exposure to high temperature. Acetylene end-capped polyimide oligomers of the type disclosed in U.S. Pat. No. 3,845,018 and U.S. Pat. No. 3,897,349 are a prime example of products having this combination of properties.
Polyimides of the type referred to above, while having excellent physical properties and good retention of these physical properties after prolonged exposure to high temperature, are subject to two recognized shortcomings. First, these polyimides must be prepared from aromatic diamines of specific structures to obtain the desired high temperature performance properties. Unfortunately, such aromatic diamines are difficult to synthesize and are expensive. In addition, the melting points of the polyimides are very close to their curing temperatures. For this reason, the polyimides are difficult to process. In particular, they are very difficult to mold.
For the above reasons, there is a continuing need in the art for heat-curable resins having good high temperature performance properties and which can be prepared at more moderate cost. In addition, there is a need in the art for resins of this type which can be more readily processed and, in particular, can be more readily molded.